Effects of ultraviolet radiation on an intertidal trematode parasite: an assessment of damage and protection.

Trematode parasites are integral components of intertidal ecosystems which experience high levels of ultraviolet radiation. Although these parasites mostly live within hosts, their life cycle involves free-living larval transmission stages such as cercariae which are directly exposed to ambient conditions. UV has previously been shown to considerably reduce the survival of cercariae. Here, we investigated potential mechanisms of protection and damage related to UV in the intertidal trematode Maritrema novaezealandensis. Firstly, the presence of sunscreen compounds (i.e. mycosporine-like amino acids) was quantified in the parasite tissue producing cercariae within a snail host, as well as in the free-swimming cercariae themselves. Secondly, levels of oxidative stress in cercariae after exposure to UV were investigated (i.e.protein carbonyls, catalase and superoxide dismutase). Thirdly, the DNA damage (i.e. cyclobutane­pyrimidine dimers) was compared between cercariae exposed and not exposed to UV. Lastly, functional aspects(survival and infectivity) of cercariae were assessed, comparing cercariae under light conditions versus dark after exposure to UV. We confirmed the presence of my cosporine-like amino acids in cercariae-producing tissue from within snail hosts, but were unable to do so in cercariae directly. Results further suggested that exposure to UV induced high levels of oxidative stress in cercariae which was accompanied by a reduction in the levels of protective antioxidant enzymes present. We also identified higher levels of DNA damage in cercariae exposed to UV, compared with those not exposed. Moreover, no clear effect of light condition was found on survival and infectivity of cercariae after exposure to UV. We concluded that cercariae are highly susceptible to UV damage and that they have very little scope for protection against or repair of UV-induced damage.

Celery (Apium graveolens L.) parenchyma cell walls examined by atomic force microscopy: effect of dehydration on cellulose microfibrils.

Atomic force microscopy (AFM) was used to image celery (Apium graveolens L.) parenchyma cell walls in situ. Cellulose microfibrils could clearly be distinguished in topographic images of the cell wall. The microfibrils of the hydrated walls appeared smaller, more uniformly distributed, and less enmeshed than those of dried peels. In material that was kept hydrated at all times and imaged under water, the microfibril diameter was mainly in the range 6-25 nm. The cellulose microfibril diameters were highly dependent on the water content of the specimen. As the water content was decreased, by mixing ethanol with the bathing solution, the microfibril diameters increased. Upon complete dehydration of the specimen we observed a significant increase in microfibril diameter. The procedure used to dehydrate the parenchyma cells also influenced the size of cellulose microfibrils with freeze-dried material having larger diameters than air-dried material.

Intra-oral temperature variation over 24 hours.

This study aimed to investigate temperature variation at archwire sites adjacent to the maxillary right central incisor and first premolar, its correlation with ambient temperature, and the influence of inter-racial variation. Twenty young adult male subjects were randomly selected (13 Asian, seven Caucasian). Thermocouples were attached to the labial archwire component of custom-made orthodontic retainers at the two intra-oral sites. A third thermocouple measured ambient temperature. A data-logger recorded temperatures at 5-second intervals over a 24-hour period. Temperatures ranged from 5.6 to 58.5 degrees C at the incisor and from 7.9 to 54 degrees C at the premolar, with medians of 34.9 degrees C and 35.6 degrees C, respectively. Ambient temperature correlated poorly with the intra-oral temperatures. The Asian and Caucasian groups had significantly different temperature distributions. On average during the 24-hour period, temperatures at the incisor site were in the range of 33-37 degrees C for 79 per cent of the time, below it for 20 per cent, and above it for only 1 per cent of the time. Corresponding figures for the premolar site were 92, 6, and 2 per cent. At both archwire sites the most frequent temperatures were in the range of 35-36 degrees C. The data presented demonstrate that the temperature at sites on an archwire in situ varies considerably over a 24-hour period and that racial differences may exist. This information should be considered during the manufacture and use of temperature-sensitive orthodontic materials, in particular nickel-titanium archwires and springs.